IGF-1 LR3

Summary

IGF-1 LR3 is an engineered version of insulin-like growth factor 1 (IGF-1, a growth factor the liver makes in response to growth hormone) designed for cell culture and animal research, with modifications that stop it binding to IGF binding proteins (blood proteins that normally hold IGF-1 in check) so more of it reaches the receptor. In rats it was about 2.5 times more anabolic (tissue building) than native IGF-1, but no human has received it in a published study, so its evidence grade is animal-only. It has never been reviewed by FDA, cannot be compounded (custom-made by a pharmacy), and IGF-1 and its analogs are prohibited by WADA under section S2, the anti-doping class for growth factors. The approved human IGF-1 product, mecasermin, is a different molecule with a narrow pediatric indication (a rare growth disorder in children).

What is IGF-1 LR3?

IGF-1 LR3 is a recombinant 83 amino acid analog of human IGF-1 with a 13 amino acid N-terminal extension and arginine substituted for glutamate at position 3, engineered in 1992 to escape IGF binding proteins. It is also known as Long R3 IGF-1, Long [Arg3]-IGF-I, LR3IGF-I, LR3-IGF-1, Long arginine 3 insulin-like growth factor 1.

How does it work?

IGF-1 activates the IGF-1 receptor to stimulate protein synthesis, cell proliferation, and glucose uptake, and inhibits protein breakdown. In blood, most native IGF-1 is bound to IGF binding proteins, which limit its free concentration and half life. LR3 IGF-1 binds those proteins very poorly, so despite binding the IGF-1 receptor about 3 fold less well than IGF-1, it is more potent in vivo because more of it is free to act. It also binds the insulin receptor, which is one basis for its hypoglycemia risk.

What does the evidence say about IGF-1 LR3?

The evidence is 1990s in vitro and rat work from the group that engineered the analog. In rat myoblasts and hepatoma cells LR3 IGF-1 was more potent than IGF-1 at stimulating protein and DNA synthesis, and in dexamethasone treated catabolic rats it was about 2.5 fold more anabolic than IGF-1 on body weight and nitrogen retention, with increased gut weight. No human study of LR3 IGF-1 exists. Human data on IGF-1 itself come from mecasermin, the FDA approved recombinant IGF-1 for severe primary IGF-1 deficiency in children, whose label documents hypoglycemia, tonsillar hypertrophy, intracranial hypertension, and a contraindication in active or suspected cancer.

Human evidence

No indexed human study of IGF-1 LR3 identified. The nearest human evidence is the labeling for mecasermin (Increlex), a recombinant native IGF-1 approved in 2005 for children with severe primary IGF-1 deficiency, which lists hypoglycemia as the most common adverse reaction and contraindicates use in active or suspected malignancy; those findings concern a different, approved molecule and a pediatric population.

Animal evidence

In L6 rat myoblasts, Long [Arg3]-IGF-1 and other N-terminal analogs were more potent than IGF-1 at stimulating protein and DNA synthesis and inhibiting protein breakdown, with the greatest advantage in cells that secrete IGF binding proteins. In dexamethasone treated rats, LR3 IGF-1 and des(1-3) IGF-1 were about 2.5 fold more potent than IGF-1 at restoring body weight and nitrogen retention, decreased muscle protein breakdown, and increased gut weight by up to 45%, despite LR3 IGF-1 binding the type 1 IGF receptor 3 fold less well.

Key studies

Conditions studied

Is IGF-1 LR3 legal in the United States?

FDA and compounding status

Never submitted to or reviewed by FDA for human use. IGF-1 LR3 is not a component of an approved drug (mecasermin is native IGF-1, a different molecule), has no USP monograph, and has not been placed on the 503A bulks list, so it cannot lawfully be compounded by 503A pharmacies or 503B outsourcing facilities. It is sold as a cell culture reagent and research chemical, which is not lawful for human use.

WADA status

WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.

Regulatory timeline

1. Sep 21, 2026WADA

   WADA publishes the 2027 Prohibited List

   WADA published the 2027 Prohibited List on September 21, 2026, and it takes effect January 1, 2027. The S2 peptide hormone and growth factor classes are unchanged. BPC-157 is still named under S0, and MOTS-c is still named under S4.4 as an activator of AMP-activated protein kinase. WADA added a note that many peptides without approval for human use fall under S0 or another section, and that a peptide not named on the list may still be prohibited. GLP-1 receptor agonists such as semaglutide and tirzepatide are still not on the list.

   Source: WADA 2027 Prohibited List
2. Jan 1, 2026WADA

   WADA 2026 Prohibited List takes effect

   The 2026 WADA Prohibited List took effect on January 1, 2026 and continues to prohibit the S2 peptide hormone and growth factor classes (GHRH analogs, growth hormone secretagogues, GH fragments, IGF-1 and analogs, MGF, thymosin beta-4 and derivatives, hCG and GnRH-class releasing factors in males), myostatin inhibitors, insulin and the AMPK activator MOTS-c under S4, desmopressin under S5, and BPC-157 under S0. GLP-1 receptor agonists such as semaglutide and tirzepatide are not on the list.

   Source: WADA Prohibited List
3. Jan 1, 2025WADA

   WADA 2025 Prohibited List keeps peptide hormones and growth factors banned at all times

   The 2025 WADA Prohibited List took effect on January 1, 2025. Section S2 (peptide hormones, growth factors, related substances and mimetics) covers GHRH analogs such as CJC-1295, sermorelin, and tesamorelin, growth hormone secretagogues such as ipamorelin, GHRP-2, GHRP-6, hexarelin, and ibutamoren (MK-677), growth hormone fragments such as AOD-9604, growth factors including IGF-1 and its analogs, MGF, and thymosin beta-4 (TB-500), and chorionic gonadotropin and releasing factors such as gonadorelin and kisspeptin (prohibited in males). Myostatin inhibitors such as ACE-031 fall under S4, insulin under S4 metabolic modulators, desmopressin under S5, and BPC-157 remains an S0 non-approved substance.

   Source: WADA Prohibited List

Full tracker for IGF-1 LR3 or the category-wide tracker.

What published studies of IGF-1 LR3 used

Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.

Not established in human literature. Rat studies used continuous subcutaneous infusion by osmotic pump at microgram per day doses scaled to 150 g animals; these do not translate to a human dose. Mecasermin, the approved native IGF-1, is dosed in children at 0.04 to 0.12 mg/kg twice daily with meals under specialist supervision, and that regimen does not apply to LR3 IGF-1.

Routes reported

IGF-1 LR3 risks and side effects

Side effects

Interactions

Contraindications

How do people access IGF-1 LR3 legally?

Typical cost: Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity.

• Rules by state
• Verified provider directory

Compare IGF-1 LR3

• IGF-1 LR3 vs PEG-MGF

What's actually offered, and what that means for you

Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make IGF-1 LR3 lawful. IGF-1 LR3 is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [4] [6]

Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [6] [7] [8] [9] [10]

What changes for you

• No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [10]
• Identity, purity, sterility, and dose accuracy can vary from batch to batch. [6]
• Insurance rarely covers it, so you usually pay cash.
• For tested athletes, IGF-1 LR3 is prohibited at all times on the WADA list, whatever the source. [5]

What to check

These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:

• A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [10]
• A real evaluation by a licensed prescriber, not just an online form.
• A certificate of analysis for the specific batch.

Frequently asked questions

Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.

From the blog

• Peptides for muscle growth, ranked by human evidence

  MK-677, sermorelin, tesamorelin, CJC-1295, IGF-1 LR3, and more ranked by human evidence. None is approved for muscle growth, and all ten are banned in tested sport.

• Peptides for tendon recovery, ranked by human evidence

  BPC-157, TB-500, GHK-Cu, PEG-MGF, and IGF-1 LR3 ranked by our evidence grades. None has a published human tendon trial. Here is the ranking, the reasoning, and what does have human data.

• What are peptides? A plain-English guide

  Peptides are short chains of amino acids. Some are FDA approved medicines, some are compounded, and many are unapproved research chemicals. Here is how to tell them apart.

Sources

Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.